Bitcoin has spawned numerous spinoffs and imitators. Why the sudden proliferation of "altcoins" – and what are the chances that any of them matter?

By David Z. Morris, contributor

FORTUNE -- Bitcoin's 2013 remains impressive, even after the digital currency has taken a serious tumble since late November – at the December 18th price of $530, a Bitcoin purchased for $13 in January would return over 4,000%.  Another explosion has tracked that price's: the emergence this year of 100 or more "altcoins," collections of code and community modeled after bitcoin and with names like Novacoin, Zetacoin, Bitbar, Cryptogenic Bullion, BBQCoin and, yes, Sexcoin.  Some offer minor but meaningful variations on bitcoin's technology, while most are outright copies – and a huge proportion are fraud schemes preying on the enthusiasm of cryptocurrency supporters.

Still, these coins are an important part of the story of bitcoin, and some are likely to be part of any future that includes cryptocurrency, a type of digital currency that depends on cryptography. Even after the recent bitcoin decline took many altcoin valuations down with it, there are five altcoins with market capitalizations of over $10 million each, another 20 of over $1 million each, and dozens of others ranging down to the aptly named "junkcoin," with a current market cap of about $75,000. Andreas M. Antonopoulos, a consultant on several bitcoin-related startup projects, author of a forthcoming technical volume on bitcoin, and host of the popular "Let's Talk Bitcoin" podcast, describes this landscape as the "crypto-currency ecosystem."

The ecological metaphor hinges in part on an evolutionary logic. "Altcoins serve two purposes," Antonopoulos says. "First, they test new tech features, showing whether they work and whether the market will accept them." Those new features mostly revolve around variations on bitcoin's mining algorithm – the "proof of work" problem-solving that secures a dis ...